This selects the point from which the ambient level is sampled. You can choose various points through the signal path on all channels. The meter is in dBu.

Gain Differential sets the difference between the ambient level (as displayed on the ambient level meter in dBu) and the 'Controlled Gain Element' fader gain level in dB as shown on the fader scales.

For example, an ambient level of -30dBu with a gain differential of 10dB will set the 'controlled gain element' fader level to -20dB on the fader scale. As the ambient level changes, the controlled fader level will 'ride' 10dB higher than the ambient level.

This selects the fader level you wish to control. Multiple input and output channel gains can be controlled by selecting an I/P or O/P group fader as the controlled element and then assigning channels to that group fader.

The min and max gain rotaries determine the operating range of the controlled fader gain level. The rate rotary determines the rate at which the controlled element gain changes in response to a change in the ambient level.

 

This selects the point from which the ANC ambient sampling and gain control program is triggered. The meter is in dBu.

When this level drops below the program gap threshold, the ANC will start sampling the ambient level and controlling the gain element.

The program gap threshold rotary sets the level below which the program gap signal must fall before the ANC starts sampling the ambient level.

The program gap time rotary determines the amount of time between the program gap signal falling below the program gap threshold and the start of ambient level sampling.

The 'Ambient Level Sampling Active' LED lights when the ANC is sampling the ambient level.

Enable the ANC. The default setting of the ANC is 'Off'. Nothing will happen to the audio in the iDR until the ANC is switched on!

Select the gain element you want to control. Typically this would be an O/P channel gain for an announcement speaker. Set max, min levels & rate if known at this stage or at least set max gain to a safe level to avoid equipment damage during set up.

Select ambient level metering point. Typically this would be source or post EQ on an input channel connected to an omni-directional mic situated in the ceiling of the ambient zone.

Adjust the mic pre to attain a low but reasonable level on the ambient meter.
Ensure that the 'Ambient Level Sampling Active' LED is lit either by raising the program gap threshold or temporarily selecting a silent program gap metering point.

It may be advisable to mute the speaker output at this point to avoid a gain loop. Adjust the gain differential such that the O/P gain is at approximately the right level when the ambient level is normal.

Select your desired program gap metering point. Typically this may be on the same channel as your ambient sensing mic or off a different mic positioned near the announcement speaker.

Set the threshold higher than the ambient level but lower than the ambient level plus announcement. This should ensure that the ambient level is not sampled as announcements are being made.

Adjust the program gap time to as high a value as is reasonable to allow echo and reverberation to die down after an announcement is made. This value can be large for occasional announcements but may have to be short if a constant audio output is being used (such as radio), to allow for an ambient sample to be made.

Optimize your system by tweaking the rotaries so that the ambient level is sampled regularly, the gain levels are satisfactory, and the announcement does not feed the ambient level when the ANC is sampling leading to feedback.